This and a companion project (Z01 HD001123) investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two species, the squirrel monkey and the common marmoset, are the main subjects of study, with additional data collected from other species where appropriate. The present project studies primate communication from a bioacoustic and ethological perspective, focusing on the detailed acoustic structure of vocalizations produced in natural settings, and the relationship of structural differences to differences in age, gender, experience and response selectivity, as well as the broader factors of social context and genetic background. Prior work in this project has determined that there is considerable individual variation in the detailed acoustic structure of infant cries, which is stable over at least the first 3 months of life. The project has also demonstrated that a Y-maze paradigm successfully permits evaluating the responsiveness of older individuals with varying experience to live infants or to recordings of infant crying. Additional experiments this year have shown that about one-third of trials, using either live infants or recorded cries, result in positive responses (approaching the sound source) from parentally experienced individuals. Another new study addressed the issue of using the most efficient method to collect vocal data from infants briefly separated from their family group for the purpose of recording their vocalizations. Prior work in our laboratory had used a very short separation time, 5 minutes, for this purpose. However, it was unclear whether the vocalizations produced during this short time period reflected the developmental state of the infant or were a reflection of a short-term emotional response to the separation. Therefore, six infants were separated for a longer period, 20 minutes, and their vocalizations analyzed. It was found that there were no significant differences in either the rate or the type of vocalizations produced in the first 5 minutes and last 5 minutes of the separation. This suggests that a 5-minute separation period is sufficient to characterize the developmental stage of an infants vocal behavior. This, in turn, means that we can continue using the less stressful, shorter separation period for this purpose.[unreadable] A detailed analysis of the infant cries of prosimian primates was completed this year. Prosimians are of interest because of the long period of separation from other primate groups evolutionarily, and the fact that several prosimians are active nocturnally. It was found that the infant cries of bushbabies are click-like in structure, very different from the tonal cries of simian primates. Furthermore, the cries of several diurnal lemurs differ in some respects from the tonal cries of simian primates. This variety of cry acoustics suggests that prosimians, being the earliest primate line, may have experimented with different types of cries. It would be of interest to investigate the laryngeal structure of these prosimians and compare them with the larynges of simian primates, as this may give important clues on the differences in cry production across the primates as a whole.